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C-Change in GEES
Human Pressures on the
Environment
Session 5: Salinization
Dr Stefan Krause, Keele University, [email protected]
C-Change in GEES: Human Pressures on the Environment – Salinization
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Dr Stefan Krause, Keele University, [email protected]
C-Change in GEES: Human Pressures on the Environment – Salinization
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Dr Stefan Krause, Keele University, [email protected]
C-Change in GEES: Human Pressures on the Environment – Salinization
Session Outline
•
The Process of Salinization
•
Human Causes of
Salinization
•
Management of Salinization
Dr Stefan Krause, Keele University, [email protected]
C-Change in GEES: Human Pressures on the Environment – Salinization
Soil Salinity
Salt affected soils are caused by excess accumulation of salts, typically most
pronounced at the soil surface.
Salts are transported to the soil surface by capillary transport from a salt laden
water table and accumulates due to evaporation.
As soil salinity increases, salt effects can result in degradation of soils and
vegetation.
Salt is a natural element of soils and water. The ions responsible for salinization
are: Na+, K+, Ca2+, Mg2+ and Cl-.
As the Na+ (sodium) predominates, a salt affected soil is often also a sodic soil.
Salinization is a natural process that results from:
•
high levels of salt in the soils.
•
landscape features that allow salts to become mobile (movement of water
table)
•
climatic trends that favour accumulation
Dr Stefan Krause, Keele University, [email protected]
C-Change in GEES: Human Pressures on the Environment – Salinization
Soil Salinity
What is Salinization?
Salinization is the process by which watersoluble salts accumulate at the surface of soil.
Salinization is a resource concern because
excess salts hinder the growth of crops by
limiting their ability to take up water.
Salinization may occur naturally or because
of conditions resulting from management
practices.
Atacama desert, salt flats
Photo: palegoldenrod (flickr.com)
Any process that affects the soil-water
balance may affect the movement and
accumulation of salts in the soil: hydrology,
climate, irrigation, drainage, plant cover and
rooting characteristics, farming practices
Dr Stefan Krause, Keele University, [email protected]
C-Change in GEES: Human Pressures on the Environment – Salinization
Soil Salinity
Salinization
In some areas (for example the Middle East, Australia)
enormous amounts of salts are stored in the soils.
Human practices have increased the salinity of top
soils by bringing salt to the surface through disrupting
natural water cycles (irrigation, land clearing, draining
etc.).
Aswan Dam
Photo: Hajor (wikimedia
commons)
One of the best examples of excess salinization was
observed in Egypt in 1970 when the Aswan High Dam
was built:
• Change in the level of ground water before the
construction enabled soil erosion
• Led to high concentration of salts in the water
table.
• High level of the water table after construction
led to the salinization of the arable land
Dr Stefan Krause, Keele University, [email protected]
C-Change in GEES: Human Pressures on the Environment – Salinization
The Salinization Process
Can occur when the water table is between two to three metres from the surface of
the soil.
The salts from the groundwater are raised by capillary action to the surface of
the soil.
This occurs when groundwater is saline (which is true in many areas), and is
favoured by land use practices, allowing more rainwater to enter the aquifer than
it could accommodate.
For example, the clearing of trees for agriculture is a major reason for dryland
salinity in some areas, since deep rooting of trees has been replaced by shallow
rooting of annual crops.
Dr Stefan Krause, Keele University, [email protected]
C-Change in GEES: Human Pressures on the Environment – Salinization
The Salinization Process
Dr Stefan Krause, Keele University, [email protected]
C-Change in GEES: Human Pressures on the Environment – Salinization
Causes of Salinization
Primary Salinization: 80% of saltaffected land has a natural origin.
Salts formed by weathering of rocks
or natural external inputs.
Secondary Salinization: 20% of
salt-affected lands, and around 15
Mha on the continent of Africa, have
a "man-made" origin. Human activity
linked to agricultural practices and in
particular to irrigation.
Flood irrigation
Dr Stefan Krause, Keele University, [email protected]
C-Change in GEES: Human Pressures on the Environment – Salinization
Causes of Salinization
Salinization on the soil surface occurs where the following conditions occur
together:
• the presence of soluble salts (sulphates of sodium, calcium, magnesium) in
the soil
• a high water table
• a high rate of evaporation
• low annual rainfall
Salinization often occurs on the rims of depressions and edges of channels, at the
base of hillslopes, and in flat, low-lying areas surrounding shallow bodies of water.
These areas receive additional water from below the surface, which evaporates,
and the salts are left behind on the soil surface.
Human practices that increase the soil moisture content (e.g. irrigation) increase
salinization as the water moves through hillslope soil, accumulates in seeps and
then evaporates.
Dr Stefan Krause, Keele University, [email protected]
C-Change in GEES: Human Pressures on the Environment – Salinization
Causes of Salinization
Irrigation
Almost all water (other than natural rainfall)
contains some dissolved salts.
Water is continually added through irrigation
and lost from the soil through
evapotranspiration and the salts that are left
behind accumulate.
Since soil salinity makes it more difficult for
plants to absorb soil moisture, these salts
must be leached out of the plant root zone
by applying additional water.
This, in turn, can lead to rising water tables,
requiring drainage to keep the saline
groundwater out of the root zone.
Dr Stefan Krause, Keele University, [email protected]
C-Change in GEES: Human Pressures on the Environment – Salinization
Causes of Salinization
Irrigation
If the water table rises too high, then natural
soil evaporation will begin to draw the salts
back upward into the soil profile.
The problem is accelerated when too much
water is added too quickly due to inefficient
water use:
• applying more water than is required for
leaching,
• using bad estimates of evapotranspiration
• poor drainage
• use of saline water for irrigating
agricultural crops.
These practices result in the concentration of
salts in the soil.
Dr Stefan Krause, Keele University, [email protected]
C-Change in GEES: Human Pressures on the Environment – Salinization
Causes of Salinization
Irrigation
Dr Stefan Krause, Keele University, [email protected]
C-Change in GEES: Human Pressures on the Environment – Salinization
Impacts of Salinization
Global Extent
Region
( FAO nomenclature)
Africa
Near East
Total
Area
Cultivated
Area
(Mha)
(Mha)
Ghana
22.8
Kenya
Country
Salt-affected Area
(Mha)
(%)
4.5
0.8
3.5
56.9
4.5
8.2
14.4
Nigeria
91.1
32.9
5.6
6.1
Tanzania
88.4
4.0
2.0
2.3
Egypt
99.5
3.3
9.1
9.1
Iran
162.2
19.4
27.4
19.9
Syria
18.4
5.2
0.5
2.7
Tunisia
15.5
4.9
1.8
11.6
Source : FAO, 2005. Integrated management for sustainable use of salt-affected soils. By A. Mashali, D.L
Suarez, H. Nabhan and R. Rabindra, FAO Soils Bulletin.
Dr Stefan Krause, Keele University, [email protected]
C-Change in GEES: Human Pressures on the Environment – Salinization
Impacts of Salinization
Global Extent
• 10 hectares of land suitable for cultivation is
lost every minute, 3 hectares of which is as a
result of salinization (equivalent to 1.5 Mha
per year).
• Today almost 400 Mha are affected by
salinization.
• In Africa almost 40 Mha are affected by
salinization, around 2% of the total surface
area.
• In the Near East almost 92 Mha are affected
by salinization, around 5% of the total
surface area.
International Commission on Water Resources Systems (2006)
Dr Stefan Krause, Keele University, [email protected]
C-Change in GEES: Human Pressures on the Environment – Salinization
Impacts of Salinization
Urban Areas
Salinity in urban areas often results from
the combination of irrigation and
groundwater processes.
Cities are often located on drylands,
leaving the rich soils for agriculture.
Irrigation is also now common in cities
(gardens and recreation areas).
Can cause yield damage to
infrastructure (roads, bricks, corrosion of
pipes and cables)
Dr Stefan Krause, Keele University, [email protected]
C-Change in GEES: Human Pressures on the Environment – Salinization
Impacts of Salinization
Vegetation
Salts in the soil increase the efforts by plant roots to take in water.
High levels of salt in the soil have a similar effect as drought - making water
less available for uptake by plant roots.
Few plants grow well on saline soils; therefore, salinisation often restricts options
for cropping in a given land area.
Salinization degrades the quality of shallow ground water and surface water
resources, such as ponds, sloughs, and dugouts.
Dr Stefan Krause, Keele University, [email protected]
C-Change in GEES: Human Pressures on the Environment – Salinization
Impacts of Salinization
The Aral Sea
Dr Stefan Krause, Keele University, [email protected]
C-Change in GEES: Human Pressures on the Environment – Salinization
Managing Salinization
Prevention of salinization by using humic acids - especially in regions where
too much irrigation was practiced.
In soils with excess salts, humic acids can fix anions and cations and
eliminate them from the root regions of the plants.
Saltbush: A type of plant that is able to tolerate saline conditions and draws
salt up into its leaves.
Saltbush
plants
nr Port
Augusta
Dr Stefan Krause, Keele University, [email protected]
C-Change in GEES: Human Pressures on the Environment – Salinization
Managing Salinization
Identifying the Problem
Early signs:
• Increased soil wetness in semiarid and arid areas
• The growth of salt-tolerant weeds
• Irregular patterns of crop growth and lack of plant vigour
Advanced signs:
• White crusting on the surface
• A broken ring pattern of salts adjacent to a body of water
• White spots and streaks in the soil
• The presence of naturally growing, salt-tolerant vegetation
Soil salinity can be estimated by measuring the electrical conductivity of the soil
solution. Electrical conductivity increases in a solution in direct proportion to the
total concentration of dissolved salts.
USDA Natural Resources Conservation Service (1998)
Dr Stefan Krause, Keele University, [email protected]
C-Change in GEES: Human Pressures on the Environment – Salinization
Managing Salinization
Reducing the severity and extent of soil salinity is primarily a
problem of water management.
Water management can be addressed in two ways:
(1) by managing the area contributing excess water to the
soil (recharge area)
or
(2) by managing the area where the excess water comes to
the surface (discharge area)
Dr Stefan Krause, Keele University, [email protected]
C-Change in GEES: Human Pressures on the Environment – Salinization
Managing Salinization
Recharge management:
• Plant crops that use the available soil moisture. Shallow rooted crops may
not extract excess subsoil moisture that can lead to salinity.
• Remove excess water from recharge areas of seeps by using actively
growing, deep-rooted plants. Perennial plants and forages, especially
alfalfa, are useful for this purpose because they have a longer growing
season and take up more water from a greater depth in the soil than annual
plants. Forages may also increase organic matter in the soil and improve
soil structure.
• Return manure and crop residue to the soil to increase soil water retention.
• Reduce summer fallow by continuous cropping.
USDA Natural Resources Conservation Service (1998)
Dr Stefan Krause, Keele University, [email protected]
C-Change in GEES: Human Pressures on the Environment – Salinization
Managing Salinization
Recharge management (cont.):
• Manage snow so that it is evenly distributed and does not pond on thawing.
• Divert surface water to down slope ponds.
• Use cropping and tillage systems that promote infiltration and permeability
e.g. building organic matter for soil aggregation and avoiding compaction.
USDA Natural Resources Conservation Service (1998)
Dr Stefan Krause, Keele University, [email protected]
C-Change in GEES: Human Pressures on the Environment – Salinization
Managing Salinization
Discharge management:
• Grow salt-tolerant crops.
• Reduce deep tillage, which may bring up salts from deeper soil horizons.
• Plant forage crops or trees next to bodies of water to increase water use.
• Install artificial drainage systems in severely affected areas only.
• Eliminate seepage from irrigation canals, dugouts, and ponds. Generally,
control measures should take an integrated approach involving cropping,
structural methods, and tillage systems.
USDA Natural Resources Conservation Service (1998)
Dr Stefan Krause, Keele University, [email protected]
C-Change in GEES: Human Pressures on the Environment – Salinization
Summary
• Salinization is a problem of global significance and one that is
rapidly growing as a consequence of human activity
• Better agricultural and land management practices are necessary to
reduce the impact of salinization
• Management efforts should focus both on recharge (the amount of
water infiltrating into the soil) and discharge (the uptake/removal of
water from the soil).
Dr Stefan Krause, Keele University, [email protected]
C-Change in GEES: Human Pressures on the Environment – Salinization
References
A. Mashali, D.L. Suarez, H. Nabhan and R. Rabindra, Integrated
Management for Sustainable Use of Salt-affected Soils, FAO Soils
Bulletin, Rome (2005)
USDA Natural Resources Conservation Service (1998) ‘Soil Quality
Information Sheet. Soil Quality Resource Concerns: Salinization’
Available at: soils.usda.gov/sqi/publications/files/salinzation.pdf
Dr Stefan Krause, Keele University, [email protected]
C-Change in GEES: Human Pressures on the Environment – Salinization
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Dr Stefan Krause, Keele University, [email protected]
C-Change in GEES: Human Pressures on the Environment – Salinization
Item Metadata
Author
Dr Stefan Krause
Stephen Whitfield
Institute – Owner
Keele University, School of Physical and Geographical Sciences
Title
Salinization Powerpoint Presentation
Date Created
January 2010
Description
Salinization – Powerpoint Presentation – Part Five of Human
Pressures on the Environment
Educational Level
1
Keywords (Primary keywords – UKOER &
GEESOER)
UKOER, GEESOER, Causes, Impacts, Management
Creative Commons License
Attribution-Non-Commercial-Share Alike 2.0 UK: England &
Wales
Dr Stefan Krause, Keele University, [email protected]
C-Change in GEES: Human Pressures on the Environment – Salinization